Suicide inactivation of cytochrome P-450 by methoxsalen. Evidence for the covalent binding of a reactive intermediate to the protein moiety

Journal Article · Fri Sep 01 00:00:00 EDT 1989 · Journal of Pharmacology and Experimental Therapeutics; (USA)

OSTI ID:5482033

Labbe, G; Descatoire, V; Beaune, P; Letteron, P; Larrey, D; Pessayre, D ^[1]

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1. Hopital Beaujon, Clichy (France)

Incubation of rat liver microsomes with (3H)methoxsalen and NADPH resulted in the covalent binding of a methoxsalen intermediate to proteins comigrating with cytochromes P-450 UT-A, PB-B/D, ISF-G and PCN-E. Binding was increased by pretreatments with phenobarbital, beta-naphthoflavone (beta NF) and dexamethasone. Such pretreatments also increased the loss of CO-binding capacity either after administration of methoxsalen, or after incubation of hepatic microsomes with methoxsalen and NADPH. Immunoprecipitation of the methoxsalen metabolite-protein adducts in phenobarbital-induced microsomes was moderate with anti-UT-A antibodies, but marked with anti-PB-B/D and anti-PCN-E antibodies. Immunoprecipitation was observed also with anti-ISF-G (anti-beta NF-B) antibodies in beta NF-induced microsomes. Methoxsalen (0.25 mM) inhibited markedly the benzphetamine demethylase activity of phenobarbital-induced microsomes and the erythromycin demethylase activity of dexamethasone-induced microsomes. Whereas methoxsalen itself did not produce any binding spectrum, in contrast either in vivo administration of methoxsalen or incubation in vitro with methoxsalen and NADPH resulted in a low-to-high spin conversion of cytochrome P-450 as suggested by the appearance of a spectrum analogous to a type I binding spectrum. This low-to-high spin conversion was apparently due to a methoxsalen intermediate (probably, covalently bound to the protein and preventing partial sixth ligation of the iron). We conclude that suicide inactivation of cytochrome P-450 by methoxsalen is related to the covalent binding of a methoxsalen intermediate to the protein moiety of several cytochrome P-450 isoenzymes (including UT-A, PB-B/D, PCN-E as well as ISF-G and/or beta NF-B).

• OSTI ID: 5482033
• Journal Information: Journal of Pharmacology and Experimental Therapeutics; (USA), Vol. 250:3; ISSN 0022-3565
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
MIXED-FUNCTION OXIDASES
ENZYME ACTIVITY
PSORALEN
BIOCHEMICAL REACTION KINETICS
CYTOCHROMES
DEXAMETHASONE
FLAVONES
HEME
IMMUNOASSAY
INHIBITION
LIVER
MICROSOMES
NADP
PHENOBARBITAL
RATS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ADRENAL HORMONES
ANESTHETICS
ANIMALS
ANTICOAGULANTS
ANTICONVULSANTS
AZINES
BARBITURATES
BIOASSAY
BODY
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CENTRAL NERVOUS SYSTEM DEPRESSANTS
COENZYMES
CORTICOSTEROIDS
COUMARINS
DIGESTIVE SYSTEM
DRUGS
ENZYMES
FLAVENOIDS
GLANDS
GLUCOCORTICOIDS
HEMATOLOGIC AGENTS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
HYPNOTICS AND SEDATIVES
ISOTOPE APPLICATIONS
KETONES
KINETICS
MAMMALS
NUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANOIDS
ORGANS
OXIDOREDUCTASES
OXYGENASES
PIGMENTS
PORPHYRINS
PREGNANES
PROTEINS
PYRIMIDINES
REACTION KINETICS
RIBOSOMES
RODENTS
STEROIDS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques